Assessment of the Applicability of Commercial Pigments for Photocatalytic Degradation of Pharmaceuticals: Comparison of Kinetics and Products of the Processes

The aim of this study was to compare the photocatalytic activity of ZnO and four inexpensive TiO2-based pigments in the degradation of tetracyclines, beta-lactams, sulfonamides and non-steroidal anti-inflammatory drugs. TiO2-P25 (Aeroxide®) was used as the reference standard catalyst. For the photocatalytic degradation of selected drugs, kinetics were determined, and intermediates were identified. Efficient drug degradation was observed in the presence of ZnO and TiO2 pigments containing only anatase. The pigment containing a mixture of anatase and rutile was practically inactive. ZnO had the highest photocatalytic activity, higher than the standard. The other pigments were found to be less active than the standard. However, the use of these pigments for drug degradation may be economically justified due to their significantly lower price than TiO2-P25 (Aeroxide®). Seventy-two drug degradation products were identified. The photodegradation process followed pseudo-first-order kinetics. It was found that the degradation products of the tested drugs are very similar regardless of the catalyst used. Only the photodegradation products of diclofenac and consequently its products were significantly different in the presence of ZnO compared to TiO2-containing photocatalysts. It was confirmed that the tested photocatalysts, with the exclusion of FS, could be useful for pharmaceutical degradation.